This invention relates to an outboard motor and more particularly to an improved exhaust system for an outboard motor.
As is well known, outboard motors present a number of design difficulties because of their very basic nature and their compact construction. The exhaust gas treatment of the powering internal combustion engines is one of the areas where there are substantial design constraints. For example, it is generally the practice to discharge the exhaust gases from the engine through an underwater exhaust gas discharge at least when traveling at high speeds so as to utilize the body of water in which the watercraft is operating as a silencing medium. However, the mere provision of an underwater exhaust gas discharge will not provide the requisite amount of silencing.
It has, therefore, been the practice to deliver the exhaust gases from the engine, which is mounted in the power head, to an expansion chamber formed in the driveshaft housing via one or more exhaust pipes. However, the provision of the expansion chamber in the driveshaft housing has a number of problems. First, the expansion chamber must have sufficient volume in order to be effective and if this sufficient volume is provided, the driveshaft housing tends to become bulky. This provides a significant problem since at least a portion of the driveshaft housing is submerged and any expansion in its size will increase the drag of the outboard motor.
Furthermore, a number of other components of the propulsion system and engine support system must pass through the driveshaft housing and the discharge of the exhaust gases to an expansion chamber formed in the driveshaft housing can give rise to certain problems with respect to heat. In addition, the relatively thin wall construction of the driveshaft housing can give rise to vibrations caused by exhaust gases and the emanation of other noises from this construction.
It is, therefore, a principal object of this invention to provide an improved outboard motor construction and specifically exhaust treatment system for an outboard motor.
It is a further object of this invention to provide an improved outboard motor construction wherein the expansion chamber for the exhaust gases is formed in the power head of the outboard motor and not in the driveshaft housing.